Monday 25 Aug
Bank Holiday heavy rainfall wash out!
Like much of the rest of England and Wales, Reigate and Surrey and the SE will see an August Bank Holiday wash-out tomorrow with lots of rain through the day, likely to be heaviest in the afternoon. This has the potential to be a moderately severe wet weather event with 48 hour rainfall accumulation possibly topping 20mm in our region with some models taking this even higher to 30-40mm in places but this is probably over-egging things. The WRF and NMM models push totals to 40-50mm in places while Hirlam and Euro4 (UKMET) keep a lid on rain at 20-30mm. Anything approaching 40mm in 48 hours would be highly unusual for us in SE in Atlantic frontal depressions but it’s by no means impossible. Remember that a “wet day” for us in the SE usually adds up to only around 10mm, so any totals over 20mm tomorrow will seem a significant deluge. Check the rogues gallery of models below for the worst rainfall offenders. By the way, always Check the UKMET forecast for a professional look at the situation, this site is for a local perspective on weather and to generate enthusiasm and interest and share some more understanding of the air around us, especially in these times of such uncertainty regarding weather and climate. As we approach another autumn and winter please share any of your weather stories and photos here or follow us @RGSweather on twitter. Twitter is an amazing portal for sharing, learning and discussing the amazing fast moving world of weather… join it if you can.
Either way, surface water local flooding is likely to be a feature on roads tomorrow and the UKMET has issued a yellow warning for heavy rain. You can expect a cloudy, dull, blustery, cool and wet day: so maybe snuggle up with the TV guide and check out some bank holiday films 🙂 and watch @RGSweather on twitter for exciting weather updates of course!
The bank holiday soaking is courtesy of a low pressure in the Atlantic set to deepen to 981mb overnight as an unseasonably fast jetstream blasting through the Channel draws very moist air from the surface and lowers the surface pressure throwing all types of fronts our way and tightening isobars cross the SE during the course of the day.
Today, the system lurked in the Atlantic as a significant band of cloud, as shown here by the VIIRS satellite at 13:00hrs.
The system will bring rain first thing tomorrow to Reigate. Initially rain looks to remain fairly light but will become progressively heavier through the day with even a low risk of heavy thundery showers as the cold front passes later pm and into Tuesday night (updated) before things gradually calm down Tues am. Whilst breezy through the day, max wind gusts are likely to arrive later in the afternoon but only 20mph. This is certainly more a wet event than a wind event!
Into Monday morning: update:
Satellite pics show a rapidly developing occluded low pressure with tightly wrapped fronts. The dark are on the sat pics represents high altitude air that is subsiding (sinking) into the depression. This dry intrusion can cause increased instability around the cold front where it is forced to rise once more nearer the surface, increasing cloud formation. Sometimes is can cause thundery doinwpours and some of the models are picking up on this by increasing rainfall totals even further for the SE as the frontal system passes over. Interestingly this does not count as a “bomb” cyclogenesis which requires a 24mb fall in pressure over 24 hours (1mb per hour). This has managed about half that pressure fall so far.